HE’S STILL GOT IT: Yankees third baseman Eric Chavez rounds the bases following his second home run off Red Sox starter Clay Buchholz. (Anthony J. Causi)

BOSTON — There have been days — too many days — when Eric Chavez’s body has felt as old as Fenway Park and as badly in need of repair.

He has been on the disabled list eight times in his career with injuries ranging from foot to neck, and plenty in between. The relentless pain and frustration has moved Chavez to stare into the abyss, to consider retirement.

But even in another DL-soiled season in 2011, Chavez found one body part in perfect working order: his baseball heart. He loved being a Yankee, adored the tradition, appreciated the expectations of winning. Chavez found joy in sharing the clubhouse with so many elite players, which was a fringe benefit he needed because he knew his body could no longer handle being full-time player. He wanted to be a vital chorus member in a winning, professional, first-class atmosphere.

So he decided he would come back in 2012 under one condition — the Yankees signed him.

It took the entirety of the offseason, but his mission was accomplished. He re-enlisted and got to experience at least one more vintage day on what was a day to honor the vintage at Fenway.

“There were times when I didn’t think there were going to be any more games like this,” Chavez said after his two homers helped the Yankees thump the Red Sox 6-2. “So, yes, it is special for me.”

Chavez contributed to the barrage of five Yankee homers that tainted Boston’s 100th-anniversary celebration of Fenway, which came replete with a homage to the past — uniforms akin to what the pre-Yankee Highlanders and Red Sox wore a century ago and 212 players from the Olde Towne Team’s history parading onto the field. Unfortunately for the Red Sox, this game was also tinged by their ugly present.

Boston is 4-9 under new manager Bobby Valentine, who is booed each time he emerges from the home dugout. Apparently the Fenway faithful must think he assembled a pitching staff that now has a 6.10 ERA.

Clay Buchholz is part of the disappointing staff, morphing into the Red Sox’s version of Phil Hughes — a young righty who has devolved from promising to puzzling. Buchholz yielded all the homers, two by Chavez and one each by Alex Rodriguez, Nick Swisher and Russell Martin.

Rodriguez’s homer was as large and historic as the day. He cleared the Monster seats to reach Landsdowne Street for his 631st homer, which moved him ahead of Ken Griffey Jr. and alone into fifth place on the all-time list. Rodriguez achieved the milestone while serving as the DH, which he is doing regularly as manager Joe Girardi tries to preserve Rodriguez’s older body.

Chavez might not be the six-time Gold Glover of his A’s past. But he still provides a way better defensive option for Girardi than the error-prone Eduardo Nunez. Still, this was just his second start, yet Girardi said, “Chavy is always ready. You never ask if he’s ready.”

That is because part of the soundtrack at Yankee Stadium is the whack, whack, whack of Chavez beginning to take extra swings in the indoor cage at home, starting in the third inning and continuing regularly the rest of games he may never even enter. Chavez has too much pride and professionalism to be unprepared for the at-bats he does get. It also has helped him retain much of the bat speed from his prime, which hitting coach Kevin Long had noticed in batting practice leading up to yesterday.

“He has been putting on a show, and I don’t just mean clearing fences by a foot or two,” Long said.

It was the power and defensive acumen that had convinced his one-time boss, A’s general manager Billy Beane, that Chavez was on a Hall-of-Fame trajectory. He signed a six-year contract. Not long after, Chavez’s body began to betray him, and he U-turned from Cooperstown to the trainer’s room.

It decimated his game so much that the two homers yesterday represented as many as he hit in 2008 and last year, and one more than he managed between 2009-10 combined.

“When I get opportunities like this, I do not want to fail,” Chavez said.

With Brett Gardner on the DL and Raul Ibanez playing more left field, Chavez should get some more opportunities. So he will keep the steady whack, whack, whack of the cage going. Staying ready. It won’t get him to the Hall, but in the here and now he is exactly where he wants to be — an important member of the 2012 Yankee chorus.